LuduminaFM-15 · FM-U5 · Planned
Momentum change and protection
Learning objectives
Calculate average force from momentum change; explain crumple zones, helmets and airbags.
8463 §§4.5.7.3 / No Trilogy counterpart
DfE single-science pp.35–37 / Combined pp.30–32. Evidence checked 30 September–1 October 2026. Skills: WS1.4,1.5,3.6; MS3b,3c.
Needs firstFM-14
Explanation
The same momentum change spread over a longer stopping time produces a smaller average force. This is why a buffer can reduce force without changing the cart’s initial momentum. Average force is distinct from peak force.
Concepts, equations and units: F_average=Δp/Δt=mΔv/Δt for fixed mass; N, kg, m/s, s; signed change.
Prediction, demonstration and game exercise
Predict, observe, explain
Stop equal-momentum carts with hard and padded barriers; compare impulse time traces.
Planned learner game exercise
Design a buffer with fixed stopping change; lengthen stopping time and inspect force.
Independent practice
Two average-force calculations and a causal protection explanation, including constraints.
Original practice example · Separate Physics Higher
A 2 kg cart slows from 5 m/s to rest in 0.50 s. Find average stopping-force magnitude.
Show working and model answer
Working / reasoning
Magnitude = mΔv/Δt = 2 × 5/0.50.
Answer
20 N opposite its initial motion.
Exit check and success criteria
Both calculations within rounding tolerance and explicit same Δp/longer time/smaller average force chain.
During practice, compare the prediction with evidence and give an error-specific prompt. The exit item uses a fresh context or fresh values, answered independently.
Misconceptions, practical links and mastery
Check these misconceptions
Padding reduces initial momentum automatically; the displayed force is necessarily peak force.
Practical preparation
Optional toy-cart/force-data analysis; no human impact trials.
Virtual preparation and revision only. Required hands-on activities and school records remain separate.
Proposed mastery
0: not yet evidenced. 1: supported. 2: independent exit criteria met. 3: successful changed-context transfer. Advance at 2; revisit with fresh retrieval. These are not GCSE grades.